A purification assembly with upstream and downstream conduits as described above is known from DE 10 2010 014 037. In this document, the first and second units for purifying the exhaust gases are placed side by side, with their respective axes substantially parallel to each other. Such an arrangement is particularly compact. On the other hand, it is necessary to conform the space connecting the upstream conduit to the downstream conduit in order to obtain a relatively uniform distribution of the exhaust gases at the outlet of the space. Moreover, an injector of a product for reducing nitrogen oxides is provided in DE 10 2010 014 037. This injector injects said product into the space. The circulation of the exhaust gases should be provided so as to ensure proper dispersion of the product within the exhaust gases.
In order to ensure the functions described above, i.e. allowing a flow of exhaust gases such that these exhaust gases are distributed relatively uniformly at the outlet of the space and ensuring proper dispersion of the injected product in the exhaust gases, two cups, one covering the exhaust gas inlet and the other one the exhaust gas outlet, are provided in the space of patent DE 10 2010 014 037. The cup covering the exhaust gas inlet has radial orifices laid out so as to orient the exhaust gases penetrating through the inlet.
Such cups generate a high counter-pressure in the exhaust line.